The present invention relates to a power transmission device for inductive energy transfer, that can operate at a wide range of voltages and that has reduced energy losses.
The principle of inductive energy transfer serves in a plurality of applications as physical basis of technical development of a large number of applications. A schematic illustration of a system for inductive energy transfer is shown in FIG. 1. An essential element in case of an inductive energy transfer is a loosely coupled conductor, which represents magnetic coupling of an inductor or a magnetic winding in the base part or charger or power transmission device 102 with an inductor or a magnetic winding in the mobile part 104 (target device). FIG. 1 (a) shows a power transmission device during operation, when energy is transferred between the base part 102 and the mobile part 104. This energy can be utilized to enable functionality of the mobile part 104. Alternatively the inductively transferred energy can be buffered in accumulator batteries (for modern applications mostly Li-ion accumulators, although further types of accumulator batteries like lead-, NiCd-, NiMh-types can be used). If the mobile part 104 is removed from the base part 102 as shown in FIG. 1b, the energy transfer is interrupted. The mobile part 104 is then supplied by the previously charged internal energy storage or remains in inactive state until the next contact with the base part 102.
When the mobile part 104 is positioned close to the base part 102, a magnetic coupling between the base part and the mobile part can be obtained so as to allow energy transfer from the base part to the mobile part. The most popular example of such an inductive charging system is the electric toothbrush, which enables contactless charging of the toothbrush as mobile part 104. In this context the term contactless is used to indicate that energy transfer can be realized without any electrical connection between corresponding electrical contacts on the mobile and the base part respectively.
Omission of electrical contacts is of great importance for many applications in different areas of application. This applies specifically to applications with high demands in the mechanical set up of the electric connections between the power source and sink in which technically complex plugs and cables can be avoided by application of inductive energy transfer (IE). Further, technical energy supply system components based on IE can be protected from environmental impacts without making the mechanical set up unnecessarily complex by appliance of outsourced connectors. Moreover, in some application areas for IE, the use of electrical connections has to be avoided in light of technical feasibility. For example, in explosion prone environments or during operation of the system components in conductive and/or aggressive media it may be technically advantageous to rely on systems that allow contactless energy transfer. Furthermore, the use of IE can improve the reliability of systems in which the devices and eventually the electrical contacts of these devices are exposed to high stresses. This is the case on the one hand for systems with rotating or moveable parts, since components based on IE allow avoiding the use of wiper contacts, which are prone to wear due to friction. In addition, IE technologies can be advantageously used in devices with connectors, which would have to be otherwise dimensioned for a plurality of plugs.
FIG. 2 shows a configuration of the power section of a system comprising a charger and a target device capable of inductive energy transfer based on a resonant DC to DC converter according to the state of the art. Besides this, further converter types based on transformers are known (flyback, forward, CUK, asymmetric half bridge etc). The input voltage Vi is cut up by a switch bridge 106 into a high frequency AC voltage. This switch bridge 106 consists of a half bridge, or full bridge, wherein semiconductor switches are used as active components. The AC voltage generated by the switch bridge is applied to the primary side of the loosely coupled transformer 110. On the primary side and the secondary side of the transformer are provided reactive components, which are schematically depicted as resonant circuits 108 and 112. As a general rule, a series capacity is integrated in the primary side although further reactive components can be provided for controlling the frequency properties of the primary circuit.
On the secondary side usage of additional reactive components can be omitted although further capacities for compensating the main inductance of the conductor can be used in parallel as well as in series circuits. Moreover, additional reactive components can be also used for controlling the frequency characteristics of the secondary side.
The secondary current is rectified on the output side at a rectifying circuit 114. The rectifying circuit 114 can be configured to perform a half way rectification or a full way rectification. The components of the rectifying circuit 114 can be conventional diodes as well as semi-conductor switches (synchronous rectification). The rectified output current is smoothed with the help of a filter 116, which can optionally include an inductance.